Tri (difluoramino) methyl bromide and process of preparation



United States Patent 3,354,217 TRI(DIFLUORAMINO)METHYL BROMIDE ANDPROCESS OF PREPARATION Charles D. Burton, Midland, Mich., assignor toThe Dow Chemical Company, Midland, Mich., a corporation of Delaware NoDrawing. Filed Feb. 2, 1966, Ser. No. 524,971 7 Claims. (Cl. 260-583)This invention relates to a novel organic fluorine nitrogen compound andmore particularly is concerned with the novel compoundtris(difluoramino)methyl bromide, F NC(NF Br, and to a method for itspreparation.

Tris(difluoiamino)methyl bromide is suitable for use as anactiveintermediate in preparing fluorine containing oxidizers employed inrocket propellant systems. In particular this novel compound findsutility in the production of stable solid oxidizers having low shocksensitivities.

Tris(difluoramino)methyl bromide has a melting point of about minus 20C., being a white solid below this temperature. In the liquid state itis colorless. Its normal boiling point, calculated from vapor pressuremeasurements, is about 71 C. It possesses a unique infrared pattern.Nuclear magnetic resonance data and mass spectroscopy analytical resultssupport the assigned structure.

This novel compound conveniently is produced by direct low temperaturefluorination of perfluoroguanidine-hydrogen bromide adduct in liquidsulfur dioxide.

In actual preparation of the compound, erfluoroguanidine and hydrogenbromide in quantities ranging from about stoichiometric of that requiredfor a 1:1 perfluoroguanidine-hydrogen bromide adduct to about 100percent molar excess hydrogen bromide or more, ordinarily fromstoichiometric to about a 25 percent molar excess and preferably about10 to about 20 percent molar excess of hydrogen bromide, are reacted inliquid sulfur dioxide at a temperature of from about minus 80 C. toabout minus 55 C., preferably at from about minus 65 to about minus 55C. Ordinarily in preparing the adduct the reaction mixture is maintainedat the reaction temperature for a period of from about 8 to about 24hours or more. In this preparation usually at a minimum a molar raito ofsulfur dioxide/perfluoroguanidine of about 1 is used. With mixtureslower in sulfur dioxide, marked reductions in yield are realized. Themaximum quantity of sulfur dioxide carrier to be employed is notcritical since excess of this solvent has no detrimental affect.Extremely large excesses of the sulfur dioxide vehicle generally are tobe avoided in order that the reaction mixture does not becomeexceedingly dilute. Extremely dilute solutions, i.e. high mole ratios ofsulfur dioxide/perfiuoroguanidine, require large storage and transportequipment. Also, the rate of reaction may be slowed down in extremelydilute solutions.

Fluorine is introduced directly into the perfluoroguanidine'hydrogenbromide adduct containing sulfur dioxide solution while maintaining thereaction mass at a temperature of from about minus 50 C. to about minus75 0., preferably at from about minus 55 to about minus 65 C. over aperiod of from about 60 minutes to about 120 minutes or more. The amountof fluorine employed at a minimum is that required to react with theadduct to give the novel compound of the present invention. Ordinarily,however, an excess of fluorine is employed as any portion of thisreactant which does not enter into the reaction readily can be recoveredand recycled for reuse. Conveniently fluorine is bubbled through thereaction mass or passed over the agitated surface of theperfiuoroguanidinehydrogen bromide adduct dissolved in the sulfurdioxide. Although fluorine can be used directly in the present process,desirably this reactant is employed in diluted form in admixture with aninert diluent gas,

3,354,217 Patented Nov. 21, 1967 followed by vapor phase chromatographyprovides an excellent means for recovering the compound.

The present process provides the following advantages; good yields oftris(difluoramino)methyl bromide are realized; no catalyst is required;and, both the intermediate perfluoroguanidine-hydrogen bromide adductand tris(difiuoramino)methyl bromide product are produced sequentiallyin the same reaction medium.

The present novel compound can be prepared in accordance with thepresent process using batch type or continuous operations. Reactors andprocess equipment to be employed are fabricated from those materialswhich are not detrimentally affected by the reactants or productmaterials and which have the requisite physical strength and desiredstructural characteristics as is understood by one skilled in the art.Stainless steel, nickel, nickel alloys and the like all are suitablematerials of construction.

The following examples will serve to further illustrate the presentinvention but not meant to limit it thereto.

Example 1.Into a 45 milliliter volume U-trap equipped with a magneticstirring bar and at a temperature of about minus 140 C. were condensedabout 0.87 gram (-13.5 millimoles) sulfur dioxide, about 0.2 gram (-13millimoles) perfluoroguanidine and about 0.12 gram (-15 millimole) ofanhydrous hydrogen bromide. The reaction mixture was then warmed toabout minus 79 C. and held at this temperature for about 16 hours. Thereduced pressure on the system was relieved with nitrogen and the sulfurdioxide solution of perfluoroguanidine-hyclrogen bromide adduct warmedto about minus 60 C.

The 1:1 perfluoroguanidinehydrogen bromide adduct Was identified by itsinfrared spectrum and nuclear magnetic resonance spectrum. It appearedto be unstable at temperatures higher than the range of from about minus50 C. to about minus 40 C.

A fluorine-nitrogen mixture containing about 33 percent by volumefluorine was passed at a total flow rate of about milliliters per minutefor a period of 120 minutes over the surface of the sulfur dioxidesolution containing the perfluoroguanidinehydrogen bromide adduct.During this time, the reaction mixture was continuously stirred. Afterthe fluorination was complete, the system was purged with dry nitrogenwhile warming the U-trap reactor to about room temperature. The productmixture which vaporized from the reactor was transferred to a collectiontrap maintained at a temperature of about minus C. Thetris(difluoroamino)methyl bromide product was collected and recovered onan 18 foot siloxane chromatographic column. The yield oftris(difluoramino) methyl bromide, based on perfluoroguanidine reactant,was about 62 percent.

Identifying characteristics of the novel compound tris(difluoramino)methyl bromide as determined analytically are as follows:

(1) Vapor pressure:

T, C. mm. Hg -20 16.2

(2) Boiling point, -7l C. (calculated from vapor pressuredeterminations).

(3) Molecular weight: Found 240, calc. 248.

(4) F nuclear magnetic resonance spectrum: One broad 2. A process forpreparing tris(difiuoramino)methyl bromide which comprises;

(a) reacting perfluoroguanidine and hydrogen bromide in liquid sulfurdioxide at a temperature of from peak at 41.4only. 5 about minus 80 C.to about minus 55 C., the 5 Mass 5 ectrum: quantities of saidperfluoroguanidine and hydrogen p e o a 0 bromide at a nnmmum beingabout stoichiornetric MIG Abundance Assignment of that required forpreparation of the 1:1 perfluoroguanidine hydrogen bromide adduct; 19548 (Fgmzm (b) introducing fluorine into the resulting sulfur di- 176 1.2F NCNFBr oxide solution containing the 1:1 perfluoroguani- 13?; 3:9dine-hydrogen bromide adduct while maintaining the 157 2.8 FzN8NI3rreaction mass at a temperature of from about minus 3:3 g 55 to aboutminus 75 C., the amount of fluorine $9 ggg 15 at a minimum being thatrequired to react with said 13,5 CNBIr adduct to providetris(difluoramino)methyl bromide,

97 34. 5 F NCNF and $3 33 FQNCN (c) separating saidtris(difiuoramino)methyl bromide g fl from the reaction mass. 50 1 3.The process as defined in claim 2 wherein the g? 23-? reaction of saidperfluoroguanidine and hydrogen bromide to prepare the corresponding 1:1perfluoroguani- (6) Infrared spectrum absorption: Absorption peaks atdn,1e hydrogen bwmlde E and the flummatwn, 935 1005 and 105 microns anda broad absorption 25 sald adduct to prepare tr1s(d1fluoram1no)methy1bromide band extending from 1105 to 112 microns is caried out at atemperature of from about minus 55 O The analytical data support theassigned structure for to minus 65 d fi d I h h dtris(difluora1nino)methyl bromide as shown directly heree process as eHE alm W 5mm y roggn i ft bromide at from about stoichiometnc to about25 per- NFz cent molar excess of that required for formation of said Fperfiuoroguanidine-l1ydrogen bromide adduct is em- 2 ployed.

NF? 5. The process as defined in claim 2 wherein hydrogen L procedureset g bromide at from about 10 to about 20 percent molar t used a i erof sepflrate runs eremt e excess of that required for formation of saidperfluoronatlon was earned out at minus 55, minus and minus uanidine hdro en bromide adduct is employed C. and fluorination times were variedfrom 60-120 g 6 Th e g as defined in claim 2 Whewin 016 minutes. In eachof these studies tris(difiuoramino)methyl i rfi bromide was recovered inhigh purity and good yields. ratio 9 su r 6 to P6 uoroguam me at aExample 3.T he procedure set forth in Example 1 40 mum 15 about was usedin a number of studies employing various sulp as defined Clalm 2ii/1161:6111 fillorlfle fur dioxide/perfiuoroguanidine mole ratios andperfiuoroleaciant 15 employed. as mlxture fluoflne Withguanidine-hydrogen bromide molar quantities. The data inert diluent 531dmixture comalnmg from about and results of these studies are summarizedin Table 1. 20 to about 40 percent fluorine on a volume basis.

TABLE 1 Mix Components Tn's(diiluoramino) Run No. methyl Bromide RemarksProduct Yield, S02 IBFG1 HBr Percent Control 0 1 1.1 0 87% PFGrecovered;

some bromine produced. 1 0.25 1 1.1 4 Small amount of Freon 114fluorocarbon added t0 provide fluidity in 1111K. 0.5 1 1.1 4 Do. 1 1 1.122 2 1 1.2 38 3 1 1.2 43 4 1 1.1 31 5 1 1.0 43 10 1 1.25 as 5 1 1.5 39 51 1. 97 34 l Perlluorognenidine.

2 Molar equivalent as based on HBr required for 1:1 PFG-HBr adduct.

3 Based on PF G.

References Cited UNITED STATES PATENTS 3,228,936 1/1966 Davis et al.260249.6

0 CHARLES B. PARKER, Primary Examiner.

CARL D. QUARFORTH, L. A. SEBASTIAN, B. BIL- LIAN, Examiners.

1. TRIS(DIFLUORAMINO)METHYL BROMIDE.
 2. A PROCESS FOR PREPARINGTRIS(DIFLUORAMINO)METHYL BROMIDE WHICH COMPRISES; (A) REACTINGPERFLUOROGUANIDINE AND HYDROGEN BROMIDE IN LIQUID SULFUR DIOXIDE AT ATEMPERATURE OF FROM ABOUT MINUS 80*C. TO ABOUT MINUS 55*C., THEQUANTITIES FO SAID PERFLUOROGUANIDINE AND HYDROGEN BROMIDE AT A MINIMUMBEING ABOUT STOICHIOMETRIC OF THAT REQUIRED FOR PREPARATION OF THE 1:1PERFLUOROGUANIDINE-HYDROGEN BROMIDE ADDUCT: (B) INTRODUCING FLUORINEINTO THE RESULTING SULFUR DIOXIDE SOLUTION CONTAINING THE 1:1PERFLUOROGUANIDINE-HYDROGEN BROMIDE ADDUCT WHILE MAINTAINING THEREACTION MASS AT A TEMPERTURE OF FROM ABOUT MINUS 55 TO ABOUT MINUS75*C., THE AMOUNT OFLUORINE AT A MINIMUM BEING THAT REQUIRED TO REACTWITH SAID ADDUCT TO PROVIDE TRIS(DIFLUORAMINO)METHYL BROMIDE, AND (C)SEPARATING SAID TRIS(DIFLUORAMINO)METHYL BROMIDE FROM THE REACTION MASS.